Evaluation of Adverse Reactions to Influenza Vaccination: A Prospective Cohort Study.

This study aimed to investigate the influence of sex, age, and quadrivalent vaccination history on adverse reactions (ARs) to influenza vaccines and the relationship between the occurrence of ARs and the risk of influenza infection. Study participants were employees of three hospitals in the Hyogo Prefecture, Japan, who received the influenza vaccine in 2019. Data were collected using questionnaires. The main factors were age, sex, and history of influenza vaccination as a control. The primary outcomes were the incidence of local and systemic ARs attributable to the vaccine and positive influenza cases among the participants during the influenza season. Logistic regression was used to calculate the odds ratio (OR) and 95% confidence interval (CI). Among the 1493 participants, 80% experienced either local or systemic ARs. ARs were less common among men than among women (OR: 0.28, 95% CI: 0.21–0.37) and less common among those aged ≥60 years (OR: 0.48, 95% CI: 0.26–0.89). ARs were significantly more likely to occur in those with a history of influenza vaccination (OR: 1.96, 95% CI: 1.15–3.33). Those who had ARs, notably localized ones, were significantly more likely to incur influenza infection. Individuals who report ARs to influenza vaccination should strictly adopt non-pharmaceutical preventive measures in the hospital, community settings, and at home.